The plot of "The Devil" tells the story of Wen Zisheng (played by Zhuang Kaixun), a violent criminal policeman. When he was investigating a case of a headless female corpse, he met the cold female forensic doctor Han Xuening (played by Shao Yuwei) who came to perform an autopsy. They found out that the deceased had undergone breast augmentation surgery at the medical beauty clinic opened by Gao Junwei (played by Fu Mengbo). Han Xuening suddenly revealed to Wen Zisheng that she had dated Gao Junwei in college and helped him to perjure a case, making Gao Junwei the number one suspect! But Wen Zisheng went to the clinic to investigate, but he felt that there were many doubts. At this time, Gao Junwei made an appointment with Han Xuening, but Han Xuening stabbed him. The complicated relationship between the two made the case more complicated and the truth could not be seen clearly...